Camping near Denver

I'm finding out the hard way that people need to make reservations well in advance if they want to camp in the mountains during summer. I don't think I emphasized this point enough--or at all--in my Moon Denver guidebook. Of course there is the wonderful and useful Moon Colorado Camping book to refer to for such needs, but I feel it will be helpful to my own readers to know more about this process. Six months ago I didn't know I wanted to take my daughter camping for her July birthday and now weekends are booked just about everywhere and first come first serve spots aren't the right option for us. So, plan ahead!